Composite sealing material

Abstract: In a composite sealing material having an inner portion (2) and a carbon outer portion (3), bulk density of the carbon outer portion is set in a range of 0.3∼2.0 g/cm³, preferably in a range of 0.5∼1.5 g/cm³, or fiber members are mixed in the carbon outer portion, or an oil layer is arranged on the carbon outer portion, or an organic layer or an inorganic layer is arranged on the carbon outer portion, so as to improve sealing properties of sealing members formed by using the composite sealing materials.

Description: Field of the Invention The present invention relates to a composite sealing material body to be used in sealing members for valves, pumps and the like. Related Art Statement Generally, valves set in pipes for steam waters, oils, chemicals and the like to be used in thermal power plants and the like, are arranged in very narrow spaces, high places, open-air spaces and the like. Therefore, it is very difficult to effect exchanging operations of sealing members of the valves. Moreover, various kinds of valves are used in the thermal power plants, and setting directions of the valves are varied as a horizontal direction, an inclined direction, a vertical direction and the like. From this point of view, it is also difficult to effect the exchanging operations of the sealing members. As the sealing members mentioned above, the composite sealing material comprising an inner portion and an outer portion enveloping said inner portion, said inner portion being composed of a small ceramic discrete material and the like, and said outer portion being composed of a carbon base material, has been disclosed in Japanese Patent Laid-Open Publication Nos. 6-58,425 and 6-87,674 (U.S. Patent Application No. 8/68,674). The composite sealing material mentioned above has at least a carbon outer portion, and thus it has sufficient sealing properties for the sealing members of the valves, the pumps and the like mentioned above, since it is easily assembled and has good sealing properties. However, if the sealing member is formed by arranging a number of the composite sealing materials in a packing box, and pressing the composite sealing materials, sometimes the sealing members have insufficient sealing properties. U.S. 2316778 discloses a metallic packing comprising metal flakes coated with graphite. DE 503861 discloses self-lubricating packing pastes containing e.g. graphite, metal, fibres, grease and oil. GB-A-2077246 discloses moldable graphite granules for producing graphite products. Summary of the Invention It is an object of the present invention to reduce or eliminate the drawbacks mentioned above and to provide a composite sealing material body having improved sealing properties. The present invention provides a composite sealing material body according to claim 1. Preferably said carbon structure has a bulk density in the range 0.3∼2.0 g/cm 3 . Preferably fibers are mixed in said carbon structure. Preferably the carbon structure is porous and an oil layer is impregnated in said porous carbon structure. By the constructions mentioned above, it is possible to improve sealing properties of the sealing members formed by using composite sealing materials, such as those which are the subject of the Japanese applications mentioned above. The composite sealing material body according to the invention can be applied to all the packing boxes into which the sealing members are to be arranged, even if dimensions of the packing boxes are varied. Therefore, in the sealing member formed by using the composite sealing material bodies, it is an advantage as compared with the conventional sealing members that it is not necessary to prepare various sealing members having dimensions corresponding to those of various packing boxes. Moreover, it is possible to control a volume reduction rate in a range of 30∼80% by controlling the bulk density of the carbon outer portion from 0.3 g/cm 3 to 2.0 g/cm 3 . Therefore, it is possible to obtain the sealing member having extremely good sealing properties. Further, if use is made of ceramics, metals, plastics and solid carbons as the inner portion of the composite sealing material body, the inner portion functions to work as aggregates. Therefore, as compared with a sealing member made of a carbon single layer, it has a good fastening stress maintaining performance. Furthermore, it is further preferred to use ceramics as the inner portion since ceramics have a good heat resistivity and show a good adhesion properties with respect to the carbon outer portion. Brief Description of the Drawings Fig. 1 is a schematic view showing one embodiment of a composite sealing material according to the invention, and Fig. 2 is a schematic view illustrating one embodiment of a packing system using the composite sealing material according to the invention. Description of the Preferred Embodiments At first, a composite sealing material disclosed in prior application and a sealing member formed by using the composite sealing materials will be explained. Fig. 1 is a schematic view showing a pellet CB as one embodiment of the composite sealing material according to the invention. The pellet CB includes a substantially spherical ceramic grain 2 surrounded with a carbon layer 3 in a spherical-cell shape. It is preferred to use a natural graphite as the carbon layer 3. The ceramic grain 2 may be composed of porcelain, alumina, silicon nitride, zirconia, carbon or the like. The diameter of the ceramic grain 2 is about more than 0.5 mm. The diameter of the pellet CB is about 1∼10 mm. Moreover, if it is assumed that a fastening stress in the formation of packing system by using the pellet CB is 200∼500 kg/cm 2 , it is preferred to use the ceramic grain 2 having a compression stress of more than 500 kg/cm 2 . Further, a thickness of the carbon layer 3 is preferably substantially equal to or greater than one-half of the diameter D of the ceramic grain 2 (t≥D/2). Fig. 2 is a schematic view showing one embodiment of a sealing member of a vapor valve used in the thermal power plants and the like, which uses a packing 11 made of the composite sealing members shown in Fig. 1. In the embodiment shown in Fig. 2, in order to seal a stem 12, the packing 11 is formed by arranging an end ring 15 on a step portion 14 of a packing box 13, arranging a number of the composite sealing members and a metal ring 16 on the end ring 15, and fixing a packing plate 17 by a number of bolts 18 to apply a stress in the packing box 13. In Fig. 2, one example of actual dimensions is as follows; stem diameter a: 20 mm, box inner diameter b: 33 mm, box width c: 6.5 mm, box depth d: 40 mm. As mentioned above, the composite sealing material body according to the invention has at least a carbon outer portion. The features of the invention are to improve the carbon outer portion. Hereinafter, the features of the invention will be explained. For the purposes of the following explanation it is to be noted that the carbon is typically in the form of graphite. Various tests were performed with respect to the packing systems using composite sealing material bodies having a carbon outer portion on/in which an inorganic layer having a solid state is arranged by coating/impregnating with an inorganic binder, or on/in which an organic layer having a solid state is arranged by coating/impregnating with an organic binder. As a result, it was understood in all the packing systems that the shape preserving performance of the composite sealing material body was improved. As for materials of the inorganic layer use is made of colloidal silica, colloidal alumina, water glass, and bentonite. As for materials of the organic layer, use is made of PVA and phenol. The inorganic layer and the organic layer can be formed by impregnating the carbon outer portion, or by spraying the inorganic binder or the organic binder on the surface of the carbon outer portion and drying it. The inorganic or organic layer may be in the solid state. Hereinafter, actual embodiments of the invention will be explained. At first, the composite sealing materials having the construction shown in Fig. 1 were prepared as the comparative example by arranging the carbon layer 3 having a thickness of 2.0 mm around the alumina grain 2 having a diameter of 2 mm. Then, coating examples in which 5 wt% of inorganic binder or 5 wt% of organic binder is sprayed and dried up to form the inorganic layer or the organic layer, were prepared. Then, the packings 11 were formed as shown in Fig. 2 by using the composite sealing members according to the comparative example, and the coating examples. After that, various packing properties of the thus formed packings 11 such as sealing performance, fastening stress maintaining performance, sliding performance of the packing, and shape preserving performance and handling performance of the composite sealing material were measured. In this case, the sealing performance means a performance for preventing a leak of a fluid (such as vapor, water, oil or the like) by the packing 11, and is estimated by an occurrence rate of fluid leak during a predetermined period. The fastening stress maintaining performance is estimated by a fastening stress after 150 hours with respect to an initial fastening stress (400 kg/cm 2 ). The sliding performance is estimated by the number of poorly operated actuators after the packing formation. The shape preserving performance means connectability of the carbon outer portion of the composite sealing material, and is estimated by a carbon weight maintaining rate after a vibration test during 3 minutes by using a rotating and tapping shaker. The handling performance of the composite sealing material means extractability from the valve, and is estimated by the measured extracting time. The results are shown in Table 1. The inorganic layer was colloidal silica, and the organic layer was polyvinyl alcohol (PVA). In each case, an alumina grain having a diameter of 2mm, with a carbon outer layer 2mm thick having a bulk density of 0.9 g/cm 3 was used. From the results shown in Table 1, it is understood that both of the coating examples show good shape preserving performance of the composite sealing material body as compared with that of the comparative example. Further, in the embodiment mentioned above, use is made of a spherical composite sealing material body, but the same results as that of the spherical composite sealing material body can be also obtained in the composite sealing material body with the other shape such as a flaky shape, and the like. In the coating example having the inorganic film or the organic film, one reason for improving the shape preserving performance of the composite sealing material body is that the crumbling of the carbon outer portion is eliminated by the formation of the solid inorganic film or the solid organic film on the carbon outer portion.

Claims: A composite sealing material body in the form of a particle having an inner portion and an outer portion enveloping said inner portion, said outer portion being composed at least of a carbon structure, characterised in that an organic material selected from polyvinyl alcohol and phenol or an inorganic material selected from colloidal silica, colloidal alumina, water glass or bentonite is present in said carbon structure. A composite sealing material according to claim 1, wherein said inner portion is made of ceramic, metal, plastics material or solid carbon. A composite sealing material according to claim 1 or 2, wherein said carbon structure is made of graphite. A composite sealing material body according to any one of claims 1 to 3, wherein said carbon structure has a bulk density in the range 0.3-1.5 g/cm 3 . A composite sealing material body according to any one of claims 1 to 4, wherein fibers are mixed in said carbon structure. A composite sealing material body according to any one of claims 1 to 5, wherein the carbon structure is porous and an oil layer is impregnated in said porous carbon structure. Use of composite sealing material bodies according to any one of the preceding claims to form a seal. A seal comprising as a sealing element a plurality of composite sealing material bodies according to any one of claims 1 to 6.

Inventors: HISHIKI TATSUYA, IKAMI TOSHIICHI, KIYOSAWA SHUNICHI, OHTA KAZUO, SEIKE SHOJI, HISHIKI, TATSUYA, IKAMI, TOSHIICHI, KIYOSAWA, SHUNICHI, OHTA, KAZUO, SEIKE, SHOJI
Applicants: NGK INSULATORS LTD, TOKYO ELECTRIC POWER SERV CO, NGK INSULATORS, LTD., TOKYO ELECTRIC POWER SERVICES CO., LTD.
Application year: 1994
Main classification: F16J15
IPC codes: F16J15